The present invention is related to electrofusion couplings for coupling a first device to a second device. The invention is particularly useful in electrofusion couplings for coupling plastic pipes to other devices, e.g., another plastic pipe, a saddle, a spigot or connector; and the invention is therefore described below particularly with respect to such applications.
Plastic pipes for conducting fluids are commonly joined by electrofusion wherein an electrofusion sleeve is applied over the pipe ends to be joined and is electrically energized to heat-fuse or weld the plastic sleeve to the pipe ends. When a plurality of pipe sections are thus joined together by electrofusion to form a continuous line, it is critical that the longitudinal axes of the pipe sections where joined together be perfectly aligned as any deviation from perfect alignment will cause the pipe sections to bend and thereby to produce tension stresses on one side of the bend and compressional stresses on the opposite side of the bend. Such bending stresses, which can result in early rupture of the plastic pipe, are frequently difficult to avoid particularly when joining together short sections of pipe, or when traversing a curve in the pipeline. In such cases, it is frequently necessary to insert specially-dimensioned angular sections or elbows to accommodate bends without introducing stresses in the joined pipe sections. This significantly increases the manufacturing costs, as well as the inventory and maintenance costs, of the pipe line.
Similar problems may also be involved where a plastic pipe is to be joined to a saddle, e.g. for receiving another plastic pipe thereacross, or where the plastic pipe is to be joined to a spigot or connector for connection to another device.